In JP-A No. 2010-112337, there is disclosed a vacuum (negative pressure pump) having a pump portion that produces negative pressure as a result of a rotational force being transmitted to it from a shaft coupled to a motive power source. This vacuum pump transmits the rotational force of the shaft to the pump portion by using a spring force to press a clutch plate attached to the distal end of a rotating shaft of the pump portion against a clutch plate attached to the distal end of the shaft.
Furthermore, in this vacuum pump, when the inside of the pump portion reaches a prescribed negative pressure, the clutch plate of the pump portion is separated from the clutch plate of the shaft by a force produced by a diaphragm, and thus energy loss caused by driving the pump portion is reduced.